Heat Of Polymerization Research Articles

Molecularly Imprinted Solid Phase Extraction Before Capillary Electrophoresis for the Analysis of Estrogens in Serum Samples

An estrogen selected molecular imprinted polymer (MIP) has been developed to be used as an alternative sorbent in solid phase extraction of serum samples before capillary electrophoresis analysis. Following a heat polymerization, MIP has been synthesized using methacrylic acid (MAA) as functional monomer, ethyleneglycol dimethacrylate (EGDMA) as crosslinker, benzoyl peroxide as radical initiator and 17β- estradiol as template, and toluene as porogen. The optimized molecular imprinted solid phase extraction (MISPE) was compared to traditional C18 solid phase extraction to purify estrogens from complex matrices. It was concluded that the MISPE system developed is useful for the selective extraction of 17β- estradiol and its major natural related estrogens, estriol and estrone, from serum samples with minimal interferences and high recoveries. Keywords: Estrogens, molecular imprinting, solid phase extraction, serum, capillary electrophoresis.

Poly(methyl-methacrylate) nanocomposites with low silica addition

Poly(methyl-methacrylate) (PMMA) represents the most popular current denture material. However, its major drawbacks are insufficient ductility and strength. The purpose of this study was to improve the mechanical properties of PMMA in denture base application by adding small quantities of nanosilica. Silica nanoparticles were added to the liquid component of the tested materials. The standard heat polymerizing procedure was followed to obtain 6 PMMA--silicon dioxide (/SiO2) concentrations (0.023%, 0.046%, 0.091%, 0.23%, 0.46%, and 0.91% by volume). Microhardness and fracture toughness of each set of specimens was compared with the unmodified specimens. Furthermore, differential scanning calorimetry and scanning electron microscopy analyses were conducted, and the results obtained were correlated with the results of mechanical properties. It was found that the maximum microhardness and fracture toughness values of the materials tested were obtained for the lowest nanosilica content. A nanosilica content of 0.023% resulted in an almost unchanged glass transition temperature (Tg), whereas the maximum amount of nanosilica induced a considerable increase in Tg. A higher Tg indicated the possible existence of a thicker interfacial layer caused by the chain immobility due to the presence of the particles. However, scanning electron microscopy results demonstrated extensive agglomeration at 0.91% nanosilica, which may have prevented the formation of a homogenous reinforced field. At a nanosilica content of 0.023%, no agglomeration was observed, which probably influenced a more homogenous distribution of nanoparticles as well as uniform reinforcing fields. Low nanoparticle content yields superior mechanical properties along with the lower cost of nanocomposite synthesis.

Preparation and properties of bisphenol A-based bisphthalonitrile polymers

The nitrile groups of 2,2-bis [4-(3,4)-dicyanophenoxy phenyl] propane (bisphthalonitrile; BAPh) can be cured by the nucleophilic phenol groups. Bisphenol A (BPA) can react with 4-nitrophathalonitrile to synthesize BAPh. Therefore, BPA was used as a novel curing agent to react with BAPh. The BAPh/BPA prepolymers and polymers were prepared by heat polymerization. The curing behaviors were characterized using differential scanning calorimetry, dynamic rheological analysis, and thermogravimetric analysis. The results indicate that BPA can decrease the melting temperature of BAPh, shorten the curing time of BAPh with lower curing temperature at 243°C, and widen the processing windows of BAPh to 95–120°C. Meanwhile, BAPh/BPA polymers could withstand temperatures up to 443°C under nitrogen atmosphere and 420°C in air when cured at 240°C for 10 h. The mechanical properties of BAPh/BPA polymers were investigated, and it exhibits a flexural strength of 75 to 122 MPa. Dynamic mechanical analysis was used to evaluate the dynamic mechanical properties of BAPh/BPA polymers. The polymers show glass transition temperature ranging from 244 to 299°C heating and cured to 240°C. Herein, the BAPh/BPA polymers can be a good candidate resin for high-performance polymeric materials.

Characterization of spontaneous collagen fibrillogenesis in a cell-free and tension-free environment

The collagen fibril packing that forms threads and bundles is poorly defined, despite the fact that it is important for distinct aspects of the adventitial and reticular dermis. The present study explored an in vitro fibrillogenesis model using the property of heat polymerization. The process was performed on glass slides with mixtures of collagen I and III, and the material was viewed by scanning electron microscopy. In all instances, collagen I and III formed fibrils with regular sizes. The formation of threads was influenced by the relative proportions of collagen I and III; increasing the relative proportion of collagen I resulted in the formation of threads showing increasing variations in thickness. These findings are in line with the differential presentation and compositions of the different parts of the dermis. The possible interventions of stromal cells and of other macromoleules of the extracellular matrix were not considered in this study.

Different Techniques in Fabrication of Ocular Prosthesis

Loss of an eye caused by cancer, trauma, or congenital defect creates a deep psychological impact on an individual's life especially social and professional life. Custom-made prosthesis, compared to stock prosthesis, provides a better fit to the eye socket, better cosmetic results, and less discomfort to the patient in the long term. The main objective of this article was to describe 3 different alternative and practical techniques of fabricating custom-made ocular prosthesis. An impression of anophthalmic socket was made with the addition of cured silicone-based precision impression material in all techniques. A master cast was prepared and duplicated with condensation silicone. A self-cure acrylic resin was polymerized in the silicone model and was fitted into the patient's eye socket. A digital photograph of the patient's iris was made using a digital camera and printed on good-quality photo paper in various shades and sizes in the first and the second techniques. Then the photo paper was coated with PVC so as not to allow any color flowing. The proper iris was then inserted to the acrylic base. The prosthesis was final processed using orthodontic heat polymerizing clear acrylic resin.In the other technique, after the trying-in process with wax pattern, an acrylic base was fabricated using heat polymerizing scleral acrylic resin. The prosthetic iris was fabricated from a transparent contact lens by painting the lens with watercolor paints and attaching it to an acrylic resin with tissue conditioner. The final process was made with heat polymerizing transparent acrylic resin. Custom-made prosthesis allows better esthetic and functional results to the patient in comparison to stock prosthesis. Further follow-up is necessary to check the condition and fit of the ocular prosthesis in such patients.

APPLICATION OF DIRECT CONTACT TEST IN EVALUATION OF CYTOTOXICITY OF ACRYLIC DENTURE BASE RESINS

The use of acrylic denture base resins is widely spread in dental practice. They belong to the group of biomaterials due to their role of morphological and functional substituent in the mouth. However, clinical practice has shown that some toxic ingredients of these materials may lead to adverse local and even systemic changes. The aim of the study was to evaluate cytotoxic effect of various denture base resins on cell culture using direct contact test. The effect of four different acrylic materials on HeLa cell structure was evaluated. Upon light microscopy analysis, MTT test was performed without previous removal of material samples. The obtained values of MTT indicate that cell proliferation is dependant on the type of acrylic denture base resins. Cold polymerization denture base resins showed mild inhibitory effect on the cell culture growth. The signs of toxicity were not observed in heat polymerization denture base resins. Acta Medica Medianae 2012; 51(1):66-72.

Evaluation of tensile bond strength of heat cure and autopolymerizing silicone-based resilient denture liners before and after thermocycling

To assess the effect of simulated mouth conditions reproduced with thermocycling on the tensile bond strength of two silicone based resilient denture liners with acrylic resin bases. Two silicone-based soft denture liners (Mollosil - Chairside autopolymerization and Molloplast B - Heat polymerization) were tested. For each liner, 30 specimens with a cross-sectional area of 10 Χ 10 mm and thickness 3 mm were processed between two acrylic blocks (Trevalon). Specimens were divided into a control group that was stored for 24 hours in water at 37°C and a test group that was thermocycled (2500 cycles) between baths of 5° and 55°C. Tensile bond strength (kg/cm²) was determined in a universal testing machine using crosshead speed of 5 mm/min. The student t-test was used to determine the significance of the difference in bond strength between the two liners. The mean tensile bond strength for control and thermocycled specimens of the two liners were: Mollosil (6.82 kg/cm² and 8.41 kg/cm²) and Molloplast-B (16.30 kg/cm² and 13.67 kg/cm²), respectively. Comparison of bond strength of control specimens with thermocycled specimens of the liners indicated a significant difference for both Mollosil (P=0.045) and Molloplast-B (P=0.027). Comparison between control specimens of both liners and thermocycled specimens of both liners indicated a highly significant difference (P<0.001). Heat polymerized resilient denture liner Molloplast-B had higher tensile bond strength than autopolymerizing liner Mollosil regardless of thermocycling. The bond strength of Mollosil increased after thermocycling while that of Molloplast-B decreased after thermocycling. Although heat-polymerized denture liners require more processing time than autopolymerizing liners, but they display much better adhesion properties to denture base resin and should thus be preferred when soft liner has to be used for a longer duration of time.

The effect of autoclave processing on some properties of heat cured denture base material

Although most of the physical and mechanical properties of denture base resin polymerized by the conventional heat polymerization have been studied, the effect of autoclave processing in these properties has not been fully determined. The aim of the present study is to investigate the effect of two different cycles of autoclave processing on the transverse strength, impact strength, surface hardness and the porosity of acrylic denture base material. Materials and methods: Vertex was the heat- cured acrylic denture base material included in the study. A total of 120 specimens were prepared, the specimens were grouped into: Control groups (Group A) in which acrylic resins processed by conventional water- bath processing technique (74°C for 1.5 hours then boil for 30 minutes) and experimental groups in which acrylic resins processed by autoclave at 121°C,210KPa.The experimental groups were divided into Group B(Fast) for15min. , and Group C (Slow) for 30min... To study the effect of the autoclave processing (Tuttnauer 2540EA), four tests were conducted transverse strength (Instron universal testing machine), impact strength (charpy tester), surface hardness (shore D), and porosity test. The results were analyzed to ANOVA and LSD test. Results: There were no significant differences between the results of the processing techniques regarding transverse, impact, and hardness tests. While, there were a highly significant difference in porosity test results. Conclusions: The autoclave processing technique might also be a good alternative to the conventional water bath processing technique. Regarding to autoclave processing technique, the slow (long) curing cycle provide better denture bases material including the tested physical and mechanical properties as compared with the fast (short) curing cycle.

Continuous Intra-Arterial Blood pH Monitoring by a Fiber-Optic Fluorosensor

Continuous intra-arterial blood pH monitoring is highly desirable in clinical practice. However, devices with appreciable accuracy are still not commercially available to date. In this study, we present a fiber-optic fluorosensor that can be used to continuously and accurately measure blood pH changes. The pH sensor is developed based on a proton-sensitive fluorescence dye, N-allyl-4-(4'-methyl-piperazinyl)-1,8-naphthalimide, which is bonded covalently to an optical fiber through heat polymerization. Fluorescence intensity was recorded after the sensor was exposed to different pH buffer solutions or intra-arterial blood in rabbits. Fluorescence intensity with emission peak at 510 nm decreased immediately as the blood pH increased. Linear and reproducible responses were observed when pH ranges from 6.8 to 8.0 with resolution of 0.03 pH units. The correlation coefficient between the pH sensor and the conventional blood gas analyzer was 0.93 in vivo ( n=75, p<0.001) with a bias and precision of -0.02 ± 0.08 pH units. The pH sensor was stable during measurement for at least 72 h. The pH sensor is not sensitive to fluctuations of various ions' concentrations and plasma osmosis at pathophysiological limits, suggesting that it is useful for the continuous measurement of blood pH at various clinical settings.

Flexural strength of direct composites submitted to post-polymerization heat

The purpose of this study was to assess the effects of post-polymerization heat on the flexural strength of direct composites. Direct composite specimens (n=10), measuring 25×2×2 mm (Z-250 and P-60), were polymerized by 3 methods: (1) light-polymerized for 40 seconds, (2) (1) + post-polymerization in an oven at 120ºC for 20 minutes, and (3) (1) post-polymerization in an autoclave at 120ºC for 20 minutes. Specimens (n=10) of the indirect composite Artglass (control group) were polymerized in a UniXS oven. Specimens were stored in distilled water for 24 hours at 37ºC and then submitted to a flexural 3-point bending test with a universal testing machine. Flexural strength (MPa) data were analyzed by one-way ANOVA and Tukey´s multiple comparison test (α=.05). Results showed that (1) additional heat polymerization in an oven provided significantly (p&lt;.05) higher flexural strengths (Z250: 158.85 MPa and P60: 147.10 MPa) than that of the Artglass resin (121.52 MPa); (2) with additional heat polymerization in an autoclave, these direct resins presented mean flexural strengths (Z250: 134.54 MPa and P60: 130.18 MPa) similar to that of Artglass (P&gt;.05); (3) groups that were only light-polymerized (Z250: 124.75 MPa and P60: 128.96 MPa) were similar to Artglass (P&gt;.05). When composites were only light-polymerized, they showed a flexural strength behavior similar to that of the indirect composite Artglass. The post-polymerization heat do not enhanced the resistance of the Filtek P60, but increased the strength of the Filtek Z250 when additional heat polymerization in a oven

Ultrastrukturelle Untersuchungen bei chronischer Rhinosinusitis ohne Polypen

Because of recurrent scarring of the ostiomeatal complex after paranasal sinus surgery the therapy of chronic rhinosinusitis without nasal polyps (CRSsNP) seems to be difficult. The aim of this study was to evaluate ultrastructural changes of nasal mucosa in patients with CRSsNP. In case of revision sinus surgery we took specimens of altered mucosa from 21 patients. All subjects suffered from recurrent CRSsNP. Twelve patients without signs of chronic rhinosinusitis dealed as control group. To prepare for electron microscopy the samples were immersed in 3% phosphate-buffered glutaraldehyde and refixed in 1% osmium acid. After dehydration and heat polymerization ultrathin cuts were prepared. After double-contrasting ultrastructures were evaluated by transmission electron microscopy. Typical changes evaluated by electron microscopy were loss of cilia, an increase of microvilli, collagen fibres, fibrocytes, fibroblasts and myofibroblasts as well as perivascular alterations and endothelial changes. The study revealed the presence of evident ultrastructural changes in the mucosa of patients with chronic rhinosinusitis without nasal polyps. Mucosal remodeling seems to be not reversible by conservative treatment.

Integrated multiscale product and process control of polymeric coating curing

In automotive coating manufacturing, control of curing of thin films of wet paint on vehicle panels is always a very challenging operational task. This is especially true when both process efficiency and product quality need to be controlled simultaneously. The challenges in this task are multiple. First, coating quality is not measurable online and its characterization is multiscale in length and time. Second, coating curing is a multistage process where heat and mass transfer and polymerization take place also in multiscale of length and time, most of which are not measurable online either. In this paper, we introduce an integrated multiscale product and process control (IMPPC) scheme that can be used to control effectively the reactive drying process. By resorting to this scheme, a set of advanced methodologies for multiscale modeling, model simplification, and multiscale controller synthesis can be seamlessly integrated to construct a high-performance control system. It is demonstrated that this control system has extraordinary performance on set-point tracking and disturbance rejection. Most importantly, it offers unique opportunities to achieve all-time on-aim control of both coating quality and process performance covering a wide range of time and length scales.

Effect of Storage Methods on Quality of Lac - A Natural Resin

A study was carried out to assess the changes in physico-chemical parameters of lac resin during storage for one year. All three forms of lac viz. sticklac, seedlac and shellac were stored following different methods as practiced by lac traders and industries, and some quality parameters of the products were evaluated during storage. Qualitative losses included decrease in flow, heat polymerization time (life) and rate of filtration; and increase in colour index and hot alcohol insolubles of lac resin during storage. In case of sticklac, maximum increase in hot alcohol insolubles (24% in ari and 69% in phunki sticklac) was noticed in samples stored in plastic bags and minimum increase (4.87 % in immature lac and 37 % in used-up broodlac) was observed in samples stored on cement floor. Very little difference in the value of flow was observed between different methods of storage. Better life and colour were observed in products stored on earthen floor. Seedlac stored on cemented floor best retained the properties i.e. minimum increase in hot alcohol insolubles (6.17%) and minimum decrease in flow (35.89%) and life (13.43%) after one year of storage. Storage in metal container resulted in 87.65% increase in hot alcohol insolubles, 61.54% decrease in flow and 19.4% decrease in life. Flow and life of cold stored shellac samples were found slightly higher (2 to 5 %) than the samples stored by other methods after one year of storage.

Effect of thermal cycling on flexural properties of carbon–graphite fiber-reinforced polymers

Objectives To determine flexural strength and modulus after water storage and thermal cycling of carbon–graphite fiber-reinforced (CGFR) polymers based on poly(methyl methacrylate) and a copolymer matrix, and to examine adhesion between fiber and matrix by scanning electron microscopy (SEM). Methods Solvent cleaned carbon–graphite (CG) braided tubes of fibers were treated with a sizing resin. The resin mixture of the matrix was reinforced with 24, 36, 47 and 58 wt% (20, 29, 38 and 47 vol.%) CG-fibers. After heat polymerization the specimens were kept for 90 days in water and thereafter hydrothermally cycled (12,000 cycles, 5/55 °C). Mechanical properties were evaluated by three-point bend testing. After thermal cycling, the adhesion between fibers and matrix was evaluated by SEM. Results Hydrothermal cycling did not decrease flexural strength of the CGFR polymers with 24 and 36 wt% fiber loadings; flexural strength values after thermocycling were 244.8 (±32.33) MPa for 24 wt% and 441.3 (±68.96) MPa for 36 wt%. Flexural strength values after thermal cycling were not further increased after increasing the fiber load to 47 (459.2 (±45.32) MPa) and 58 wt% (310.4 (±52.79) MPa). SEM revealed good adhesion between fibers and matrix for all fiber loadings examined. Conclusions The combination of the fiber treatment and resin matrix described resulted in good adhesion between CG-fibers and matrix. The flexural values for fiber loadings up to 36 wt% appear promising for prosthodontic applications such as implant-retained prostheses.

Microwave step‐growth polymerization of 5‐(4‐methyl‐2‐phthalimidylpentanoylamino)isophthalic acid with different diisocyanates

AbstractThe utilization of microwave energy in polymer synthesis is a fast growing field of research leading to a more rapid and cleaner polymerization process. In order to synthesize novel optically active monomer 5‐(4‐methyl‐2‐phthalimidylpentanoylamino)isophthalic acid (6), the reaction of phthalic anhydride with l‐leucine was carried out in an acetic acid solution and 4‐methyl‐2‐phthalimidylpentanoic acid as an imide acid was obtained in good yield. Then, it was converted to 4‐methyl‐2‐phthalimidylpentanoyl chloride by treatment with thionyl chloride. This acid chloride was reacted with 5‐aminoisophthalic acid and the novel bulky aromatic amide‐imide chiral monomer 6 was obtained in high yield and was characterized with spectroscopy techniques as well as specific rotation and elemental analysis. Polycondensation of monomer 6 with different diisocyanates such as 4,4′‐methylenebis(phenyl isocyanate), toluene‐2,4‐diisocyanate, isophorone diisocyanate, and hexamethylene diisocyanate was performed by two different methods: microwave irradiation and classical heating polymerization techniques in the presence of various catalysts and without a catalyst. The microwave polymerization technique provides a new way for the production of polymers at high rates. The resulting novel optically active polyamides have inherent viscosities in the range of 0.25–0.63 dl/g. They show good thermal stability and are soluble in amide‐type solvents. The obtained polyamides were characterized by FT‐IR, 1H‐NMR spectroscopy, elemental analyses, specific rotation, and thermal analyses methods. Copyright © 2008 John Wiley &amp; Sons, Ltd.

Three dimensional changes in maxillary complete dentures immersed in water for seven days after polymerization

The purpose of this study was to investigate the three dimensional changes in the fitting surface and artificial teeth of maxillary complete dentures which were fabricated using two different polymerizing processes: heat polymerization (HP) and microwave polymerization (MP), after immersion in water for seven days. The amount of distortion in the molar region of the alveolar ridge was significantly different between HP and MP. However, the overall distortion of the dentures polymerized using both methods was similar. The distortion due to immersion in water for seven days compensated for the polymerization distortion, but the amount of distortion was very slight.

Effect of Polishing Technique and Brushing on Surface Roughness of Acrylic Resins

This study evaluated the abrasion resistance of acrylic resin to routine dental brushing procedures using different dentifrices after the resin surface had been chemically or mechanically polished. Eighty specimens were prepared using heat-polymerizing (HP) and autopolymerizing (AP) acrylic resin, and immediately submitted to grinding with abrasive stones and disks. The specimens were divided into two groups: the first group was mechanically polished (MP) using pumice slurry, and the second group was chemically polished (CP) using heated monomer. After polishing, the specimens were submitted to 30,000 brushing cycles. Surface roughness was measured after polishing and brushing procedures, using a Surfcorder SE 1700 rugosimeter. Data were statistically analyzed by ANOVA (alpha= 0.05). There were significant differences in surface roughness between polishing with MP and CP (p < 0.05). Significant differences in surface roughness were also found between brushing with MFP dentifrice and Tartar Control dentifrice (p < 0.05). MP produced smoother surfaces than CP, and surface roughness as a result of polishing technique was not influenced by acrylic resin type. Even though MP resulted in smoother surfaces initially, subjecting the acrylic resin to dentifrice brushing negated this advantage.

Visualization of micromorphology of leaf epicuticular waxes of the rubber tree Ficus elastica by electron microscopy

Ultrastructural aspects of leaf epicuticular waxes were investigated in Ficus elastica by scanning and transmission electron microscopy. Glossy leaves of the rubber tree were collected and subjected to different regimes of specimen preparation for surface observations. F. elastica leaves were hypostomatic and stomata were surrounded with a cuticular thickening that formed a rim. The most prominent epicuticular wax structures of F. elastica leaves included granules and platelets. Without fixation and metal coating, epicuticular wax structures could be discerned on the leaf surface by low-vacuum (ca. 7 Pa) scanning electron microscopy. In terms of delineation and retention of the structures, the combination of vapor fixation by glutaraldehyde and osmium tetroxide with subsequent gold coating provided the most satisfactory results, as evidenced by high resolution and sharp protrusions of epicuticular waxes. However, erosion of epicuticular wax edges was noted in the immersion fixed leaves, showing less elongated platelets, less distinct wax edges, and granule cracking. These results suggest that the vapor fixation procedure for demonstrating three-dimensional epicuticular wax structures would facilitate characterization of diverse types of waxes. Instances were noted where epicuticular waxes grew over neighboring epidermal ridges and occluded stomata. In cross sections, epicuticular waxes were observed above the cuticle proper and ranged approximately from 100 nm to 500 nm in thickness. The native leaf epicuticular waxes had many layers of different electron density that were oriented parallel to each other and parallel or perpendicular to the cuticle surface, implying strata of crystal growth. Such retention of native epicuticular wax structures could be achieved through the use of acrylic resin treated with less harsh dehydrants and mild heat polymerization, alleviating wax extraction during specimen preparations.

Porosity of different thickness of acrylic polymerized by different methods.

Aims: To evaluate the porosity that occur in the acrylic resin denture base polymerized by the microwave cycle and conventional water bath with two different thickness, relation between the thickness of specimen and its percentage of porosity. Material and methods: Forty rectangular resin specimens with the following dimensions (65×40×6mm), (65×40×3mm) were subdivided according to polymerization method into microwave cycle and conventional heat polymerization method to obtain 10 specimens with different polymerization method and thickness, for each one of 4 groups. Porosity was calculated by measure the specimen volume before and after its immersion in water, data were analyzed by student t–test analysis at ( p< 0.05). Results: Showed that specimens of (6mm) that cured by microwave polymerization method showed significantly higher percentage of porosity when compared to the same thickness of conventional water bath polymerized acrylic resin at (p<0.05), while no significant difference between the percentage porosity of the conventional and microwave heat cured acrylic resin of (3mm) thickness specimens. Also there is no significant difference between the thickness of specimen and the conventional water bath method of heat cured acrylic resin. While for microwave curing method of heat cured acrylic resin there is significant difference for increase of percentage of porosity with increase of thickness of specimens. Conclusions: The conventional acrylic resin of (≥3mm) specimens thickness can be polymerized with microwave curing method safely with less porosity , while for (≥ 6mm) specimens thickness is preferred to be polymerized by conventional water bath curing method

A comparison of three dimensional change in maxillary complete dentures between conventional heat polymerizing and microwave polymerizing techniques

The purpose of this study was to measure and compare two different polymerizing processes, heat polymerizing (HP) and microwave polymerizing (MP), on the three dimensional changes in the fitting surface and artificial teeth of maxillary complete dentures. A threedimensional coordinate measurement system was used to record distortion of the specimens. The distortion of the fitting surface was measured from the reference plane on the fitting side from which a coordinate system was set, and the movement of the artificial teeth and the distortion of the polished surface was measured from the reference plane of the artificial tooth side, from which a coordinate system was set. It was clearly showed that various distortions of denture specimens after polymerization process can be measured with this three-coordinate measuring machine. The study showed that the overall distortion of the fitting surface in HP specimens was shown to be larger than in MP ones.